Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already provide readOnlyHint, idempotentHint, and destructiveHint, but the description adds valuable behavioral context: anonymity, no account/location lookup, EUR units, TAN as percent, and the critical caveat that omitted fields use published illustrative defaults rather than known user facts. This goes meaningfully beyond the annotations and helps the agent set correct expectations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Four sentences, each earning its place: the first states the core purpose and outputs, the second clarifies privacy/read-only nature, the third resolves unit ambiguity, and the fourth flags the default-value behavior and instructs the agent to include assumptions. The description is dense but well-organized and free of filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For an 11-parameter simulation with an output schema, the description covers what the tool does, the scope of costs, key behavioral caveats (defaults, units, anonymity), and what to include when presenting results. Since an output schema exists, return-value detail is not needed in the description, so nothing essential is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds cross-cutting parameter semantics: all monetary amounts are in EUR, annual_rate is in percent TAN rather than TAEG, and omitted inputs fall back to illustrative defaults. This complements the per-parameter schema descriptions and reduces the chance of unit or default misreadings.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description uses a specific verb ('Estimate') with a precise resource ('Portugal residential purchase costs') and enumerates the exact outputs (IMT, youth relief, stamp duty, loan payment, savings shortfall, effort rate, rate scenarios, annual amortisation). This clearly differentiates it from sibling tools like casatoo_search_listings and casatoo_get_listing, which are about finding and viewing listings.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description communicates clear context for when to use the tool: estimating purchase costs with Casatoo's logic, anonymously, without account or location lookup. It implies this is for illustrative calculations rather than obtaining real user-specific data, but it does not explicitly name alternatives or state 'use this when...' versus other tools.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.